1. Field of the Invention
The present invention relates to a projection type display apparatus.
2. Description of the Related Art
A color projection display apparatus is an apparatus which displays a color image on a screen by color-separating a white light beam into color light beams of R (red), G (green) and B (blue) as three primary colors and guiding the same to spatial light modulators respectively corresponding thereto, color-synthesizing the color light beams, which have been optically modulated by the spatial light modulators of the three primary colors in accordance with video signals, and projecting the same by a projection lens.
As for an optical appliance, it is known that such a problem arises that the focusing performance of a lens to be used deteriorates due to temperature change in use environment.
Furthermore, since a color projection display apparatus uses a high output light source lamp for directing a strong light beam to the optical system, the thermal expansion is brought about in a supporting member for supporting the projection lens according to the temperature rise of the projection display apparatus generated after turning on the power source of the apparatus so that a problem occurs that the focusing performance of the projection lens deteriorates according to the change of a distance between each spatial light modulator and the projection lens with the passage of time.
As a video projector capable of preventing the deterioration of focusing performance of the projection lens caused by the temperature change at the time of operating the projection display apparatus, the Japanese Patent Application Laid Open (JP-A) No.9-90273 discloses a lens focusing device. In a projection type television for enlarging an image displayed on a cathode ray tube (CRT) and then projecting the enlarged image on a screen by a projection lens, a part of the projection lens is provided reciprocally movably in the optical axis direction by a slight amount by optical coupling by filling the space between the projection lens and the CRT with a liquid having a refractive index close to that of the face glass of the CRT and high transparency so that a focusing correction may be executed against temperature drift.
Moreover, the Japanese Patent Application Laid-Open (JP-A) No.8-160276 discloses a lens containing member with a focus correcting function. An optical appliance having a wide range of temperature change of use environment includes a lens barrel fixed on an optical appliance main body having a light receiving member. Furthermore, the optical compliance is provided with another lens barrel that surrounds its housing and supports a lens system for focusing on the light receiving member. The two lens barrels are connected to each other with a connection member having a thermal expansion coefficient larger than that of each lens barrel so that a lens containing member can correct a focus shift due to temperature change.
As mentioned above, since a color projection display apparatus uses a high output light source lamp, there is the following problem peculiar to the configuration of the projection display apparatus. That is, the temperature around the apparatus rises rather due to the internal light source lamp with the passage of time after turning on the power source of the apparatus than the environment temperature change surrounding the apparatus so that it causes the thermal expansion of optical members and a supporting member for supporting a projection lens inside the apparatus, and as a consequence the distance between each spatial light modulator and the projection lens changes with the passage of time so as to provide a main cause of deterioration in focusing performance of the projection lens.
Therefore, it is difficult to correct focusing against the temperature drift in the projection display apparatus by the configuration of including the entire apparatus in the lens containing member as proposed in the above-mentioned Japanese Patent Application Laid-Open (JP-A) No.8-160276, or by the configuration of improving the coupling of the optical members as proposed in the above-mentioned Japanese Patent Application Laid-Open (JP-A) No.9-90273.
The present invention has been achieved in view of the above-mentioned problems, and accordingly an object thereof is to provide a projection type display apparatus using a high output light source lamp, capable of projecting a high quality image with a constantly optimum focus by canceling a fluctuation of distance between a spatial light modulator and a projection lens due to heat generated by a light source lamp at the time of operating the projection type display apparatus and temperature change in a use environment.
In order to achieve the above-mentioned object, there is provided a projection type display apparatus comprising: a spatial light modulator for optically modulating an input image to obtain an optical image to be projected; a projection lens; an optical member with the spatial light modulator fixed, for guiding the optical image to an incident side of the projection lens; a first supporting member having a first thermal expansion coefficient; and a second supporting member having a second thermal expansion coefficient larger than the first thermal expansion coefficient, wherein the optical member is fixed on a first end part of the first supporting member in a part not to block the optical image emitted from the optical member to the incident side of the projection lens, and the longitudinal direction of the first supporting member with the optical member fixed is provided parallel to the optical axis of the projection lens; a first end part of the second supporting member is fixed to a second end part of the first supporting member, the second end part being disposed at a position facing the first end part; a second end part which is an end part opposite to the first end part of the second supporting member is fixed to an incident side end part of the projection lens, and an optical axis of the projection lens and an axis of a light beam emitted from the optical member are parallel; the second end part of the second supporting member is disposed on an optical member side with respect to the second end part of the first supporting member; and a thermal expansion amount of the first supporting member from the first end part to the second end part thereof offsets a thermal expansion amount of the second supporting member from the first end part to the second end part thereof.
According to a preferable embodiment of the present invention, the lengths L1 and L2 are set to satisfy L1xc3x97k1=L2xc3x97k2, where L1 is a length from a projection lens side end face of the optical member which emits the optical image to a position at which the second end part of the first supporting member is attached to the first end part of the second supporting member; L2 is a length from a position at which the second end part of the first supporting member is attached to the first end part of the second supporting member, to a position at which the second end part of the second supporting member is fixed to the incident side end part of the projection lens; k1 is the first thermal expansion coefficient; and k2 is the second thermal expansion coefficient.